Disclosed herein is an optical cable for avionics applications, methods of manufacture thereof and articles comprising the same. More specifically, disclosed herein is an optical cable connection for use in avionics applications, methods of manufacture thereof and articles comprising the same.
Optical fibers used in optical applications generally have to meet the requirements of ARINC (Aeronautical Radio, Incorporated) 802. ARINC 802 provides specifications that cover the performance requirements, dimensions, quality assurance criteria, test procedures, and cable codification for fiber optic cables that are suitable for use in commercial aircraft. In order to meet the requirements of ARINC 802, a ruggedized simplex loose tube structured cable is used.
FIG. 1 depicts a cross-section of a cable connection 100 used in installations where resistance to cable clamping and resistance to cable elongation loads are desirable. The ruggedized simplex loose tube structure cable 100 comprises an unbuffered optical fiber 102 upon which is disposed a cladding 103 and a soft, loose buffer sleeve 104 (hereinafter buffer sleeve 104). The buffer sleeve 104 generally comprises a polymeric material. In comparative commercially available optical cables, the buffer sleeve 104 generally comprises a soft polytetrafluoroethylene (PTFE) tape loose buffer within which the optical fiber 102 with the cladding 103 disposed thereon can flex when subjected to compressive forces.
A first reinforcing layer (also termed a first strength member layer) 106, an inner jacket 108, a second reinforcing layer (also termed a second strength member layer) 110 and an outer jacket 112 are disposed in succession on the buffer sleeve 104. The first and second reinforcing layers generally comprise woven fibrous yarns in order to provide strength and reinforcement to these layers.
The use of the second reinforcing layer and the second outer jacket increase the cable diameter and weight. Optical cables of this configuration typically have an outer diameter of 2.85 millimeters and a weight of 12 kg/km. It is desirable to avoid this increase in size and weight for the cable. Moreover, the polymer material selected for the buffer sleeve has to be soft to allow for longitudinal compression of the tube when a spring loaded ferrule of the connector is compressed when mated to system components.
FIG. 2 depicts a side view of a portion of the end of the cable 100 of the FIG. 1 with a pull-proof connector 118 that is used in avionics applications. The pull-proof connector 118 is generally fitted with a ceramic ferrule (shown and detailed in the FIGS. 3A and 3B below). In the FIG. 1, a portion of a cable 100 comprising the unbuffered optical fiber 102 is in communication with the pull-proof connector 118. The pull-proof connector 118 comprises a socket 116 into which fits the ceramic ferrule (shown in the FIGS. 3A and 3B). The pull-proof connector may be formed by the portions of the cable that lie outside of the soft, loose buffer sleeve 104.
FIG. 3A depicts the ceramic ferrule 200 that is part of the pull-proof connector 118 in a non-compressed position, while the FIG. 3B depicts the ceramic ferrule 200 in a compressed position.
The ceramic ferrule 200 shown in the FIG. 3A comprises a male connector annular plug 202 (hereinafter plug 202) that mates with the socket 116 to form the pull-proof connector 118. The annular plug 202 comprises a guide tube portion 210 that fits around the outer jacket of the optical cable 100. The guide tube portion serves as a location element for positioning the plug to be annular with the optical cable 100. Disposed in the plug 202 is a ferrule 206 that contains a first hollow portion 204 that accommodates the buffer sleeve 104. In the first hollow portion 204, it may be seen that a portion of the optical fiber is unsupported by the buffer sleeve 104. The head of the ferrule 206 comprises a second hollow portion that accommodates the optical cable 102. An epoxy plug 208 encapsulates the optical fiber at the point that it enters the second hollow portion 205 of the ferrule that accommodates the optical cable 102. The epoxy plug 208 behaves as a sealant.
The portion of the optical fiber is unsupported by the buffer sleeve 104 occurs because assembly manufacturers encounter difficulties in right-sizing the current simplex loose structure cable. Specifically, the buffer sleeve must contact the bottom of the male connector plug 202 where the ceramic ferrule is located as shown in FIG. 3A. However, it is not always possible to size the buffer sleeve accurately to precisely contact the bottom of the male connector plug 202 in the compressed position.
In the non-compressed position depicted in the FIG. 3A, a portion of the ferrule 206 protrudes outside the plug 202 while the first hollow portion 204 accommodates the buffer sleeve 104 and the second hollow portion 205 accommodates the optical fiber 102 without any significant stresses on either the buffer sleeve 104 or the optical fiber 102.
In the compressed position depicted in the FIG. 3B, the ferrule 206 is pressed into the plug 202. During the compression or thereafter, the optical fiber 102 sometimes undergoes buckling 211 in the unsupported portion because of compressive stresses. It has been observed that the optical fiber 102 will often undergo buckling and break if not protected by the buffer sleeve 104 when the ferrule 206 is compressed and decompressed during connection to system components.
In addition, during compression, the epoxy plug 208 often contacts the buffer sleeve 104 and wicks into it upon contact. FIG. 4A depicts the wicking 302 of the epoxy plug into the buffer sleeve 104. Once the epoxy enters the buffer sleeve 104 and bonds the coated optical fiber to the buffer sleeve 104, movement of the coated optical fiber within the buffer sleeve 104 is inhibited, resulting in a high stress level that frequently leads to optical fiber breakage.
In the FIG. 4B, kinking 306 of the buffer sleeve is observed within the connector body as the spring loaded ferrule retracts. The spring loaded ferrule is designed to retract a minimum of 1.5 mm and the simplex buffer sleeve buffered cable must take up or compensate this retraction (compression of spring loaded ferrule) without breakage of the optical fiber, repeatedly, many times over the life of the terminated cable assembly. The kinking of this soft buffer sleeve, required to protect the coated optical fiber, results in frequent fiber breaks at this point of kinking. Also, because the buffer sleeve is soft, the strength member yarns radially compress the tube as they move to the center of the cable structure when under load. This results in excessive cable elongation under cable tensile load, causing additional fiber breakage.
It is therefore desirable to manufacture optical cables for avionics applications that do not suffer from the aforementioned drawbacks.